The subject matter disclosed herein relates to steam turbines and, in particular, to providing cooling to rotors of the turbine during operation.
In power generation systems where waste heat from one portion is used to heat steam in a steam turbine (e.g., a combined cycle power plant (CCPP), or multi-stage steam turbine), the first portion generates waste heat and the steam turbine recovers that heat to produce electricity. For example, in a CCPP a gas turbine generator generates electricity and the waste heat is used to make steam to generate additional electricity via a steam turbine. Utilizing the waste heat to make steam for use in a steam turbine enhances the efficiency of electricity generation.
An increase in temperature of the steam passing into an inlet throttle of a steam turbine has been shown to have a direct effect on the efficiency of entire CCPP. Indeed, an increase in the steam inlet temperature of around 50° F. attributes to a considerable increase in the plant efficiency. Experience has shown, however, that even 50° F. increase in the steam temperature may affect the steam turbine's rotor life.
The problem is usually overcome by using more temperature resistant rotor material. Such a solution, however, typically increases costs.